The source-date code on a pot is a 6 or 7 digit code impressed
into the casing of the potentiometer. For speakers this code can be
5, 6, 7 or 8 digits long, and it's ink-stamped or
paint-stamped on the "bell housing" of the speaker.

In either case, the code works the same. The first 3 digits on a pot,
or the first 2, 3 or 4 digits on a speaker are the source or manufacturer
code.

The remaining 3 or 4 digits are the date code. In 3 digit dates code,
the 1st digit is the last digit of the year. On 4 digits date
codes, the 1st and 2nd digits are the last two digits of the year.
In either case,
the remaining 2 digits are the week of manufacture (01 to 52). With
this in mind, remember if the last two digits of the source-date code
are greater than 52, you're not looking at the source-date code!

Also it's worth mentioning:

Sometimes there is a space or hyphen between the manuafacturer
code and the year/week code.

3 digit date codes were used in the 1940's and 1950's.

4 digit date codes were used in the 1960's and later (this makes
determining the year much simplier!).

On 3 digit date codes, you have to "guess" the decade of the pot or
speaker. Usually this isn't too difficult.

Examples of Source-Date Codes.

With all this information in mind, can you identify the following
manufacturer and date of these source-date codes?

220 7001

Jensen speaker, 1st week of 1970.

137341

CTS, 41st week of 1953 (or 1943 or 1963, but probably
1953 as source-date codes weren't used much during or before WWII, and
4 digit date codes weren't used till the 1960's and later).

304-6110

Stackpole pot, 10th week of 1961.

137848

CTS, 48th week or 1948 or 1958.

4656755

Not a source-date code. Can you see why?
If you can't, read the above information again!